This invention relates to process for the development of imagewise exposed photographic recording materials, more particularly to a high speed process in which the materials are developed in a redox developer/amplifier solution.

Redox amplification processes have been described, for example in British Specifications Nos. 1,268,126; 1,399,481; 1,403,418; and 1,560,572. In such processes colour materials are developed to produce a silver image(which may contain only small amounts of silver) and treated with a redox amplifying solution (or a combined developer/amplifier) to form a dye image.

The developer-amplifier solution contains a colour developing agent and an oxidising agent which will oxidise the colour developing agent in the presence of the silver image which acts as a catalyst.

Oxidised colour developer reacts with a colour coupler to form the dye image. The amount of dye formed depends on the time of treatment or the availability of the colour coupler and is less dependent on the amount of silver in the image than is the case in conventional colour development processes.

Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide and compounds which provide hydrogen peroxide, e.g. addition compounds of hydrogen peroxide such as perborates and addition compounds of hydrogen peroxide with urea.

Other oxidizing agents include cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used.

In colour photography development (whether redox or conventional) it is necessary at an appropriate stage to remove the silver image which, if left behind would darken the dye image. Also it is necessary to remove unused silver halide because it darkens on exposure to light. To remove the silver the practice has been to convert the silver to silver halide with a suitable oxidizing agent known in the art as a bleach and then remove the silver halide with a fixing agent.

Suitable oxidizing agents are potassium ferricyanide, or ferric iron complexed with ethylene diamine tetraacetic acid acting in the presence of potassium bromide. The two steps may be combined using a solution called a bleach-fix or blix.

In the case of a bleach-fix employed after a redox amplification the solution only needs small amounts of iron (III) and thiosulphate because there is usually only a small amount of silver to remove.

United States Patent No 5,200,301 relates to a colour photographic silver halide material which is particularly suitable for coloured machine readable identification systems. Machine-readable detection systems normally operate by I.R. absorption of the data applied and this patent is concerned with the problem of providing a colour photographic material which produces a clear brilliant dye image and also shows adequate I.R. absorption in the data part, the I.R. zones being photographically produced. Although directed to a different problem from that with which the present invention is concerned, a process for the redox development of photographic materials containing greater than 300mg/m² of silver is described in which the development stage is faster than conventional. A subsequent fixing step is disclosed but there is no bleaching step with the result that the silver is left in the developed photographic material.

Redox development/amplification is intended primarily for photographic materials containing low amounts of silver, especially for low silver photographic papers i.e. containing less than 300mg/m² of silver.

The time of development using a redox system with low silver photographic paper is broadly similar to that for a conventional development process applied to conventional i.e higher silver-containing materials.

However it is very desirable to be able to reduce the development time because this enables more photographic material to be processed with existing processing equipment or for the processing equipment to be made smaller.

A solution to this problem has now been invented by a process in which a developer/amplifier solution containing an oxidizing agent is used for the development/amplification of photographic recording material containing more than 300mg/m² of silver and in which the time of the development/amplification is less than 15 seconds.

According to the present invention a process for the development of an imagewise exposed photographic recording material containing more than 300mg/m² of silver comprises subjecting the photographic recording material to a development/amplification step using a developer/amplifier solution containing as the oxidizing agent, Hydrogen peroxide and controlling the process temperature within the range 20 to 50°C, preferably 27 to 45°C and the process time being between 5 and 15 seconds preferably 7 to 15 seconds.

The development time is reduced. This means that the processor can be made smaller or, alternatively, the processor can be made more productive. Further the problem of staining which has been found to occur when a bleach-fix of conventional concentration follows the development/amplification has been avoided.

A bleach-fix step preferably follows the development/amplification step and preferably employs a bleach-fix solution which contains iron (III) in concentration of from 0.02 to 0.5 moles per litre as the oxidant and a mixture of thiosulphate and sulphite (or metabisulphite) in amounts such that the concentration of thiosulphate is from 0.05 to 1 molar.

Preferably the amounts of iron (III) complex and sulphite (or metabisulphite) added to make up the solution are from 0.015 to 0.3 moles of iron (III) complex and from 0.05 to 0.5 moles of sulphite.

Preferably the bleach-fix step immediately follows the redox development amplification step. By immediately we mean without any intervening treatment or step.

By process time we mean the time the photographic material is in the relevant solution, for example, the time of the redox development is the time measured in seconds that the photographic material is in the developer/amplifier solution.

The temperature of the bleach-fix solution is preferably from 24 to 50°C more preferably from 30 to 45°C.

The oxidizing agent in the development/amplification is hydrogen peroxide or a compound that generates hydrogen peroxide and the hydrogen peroxide is preferably present in amounts from 0.5 to 15ml/l more preferably 0.5 to 5ml/l and especially from 0.5 to 2.0ml/1 (as 30% w/w aqueous solution).

Preferably the silver halide in the photographic material is substantially all silver chloride.

The colour developing agent may be any of those known in the art, for example, the p-phenylene diamines eg:

• 4-amino N,N-diethylaniline hydrochloride,
• 4-amino-3-methyl-N,N-diethylaniline hydrochloride,
• 4-amino-3methyl-N-ethyl-N-(beta-(methanesulfonamido) ethyl)aniline sesquisulphate hydrate,
• 4-amino-3-methyl-N-ethyl-N-(beta hydroxyethyl)aniline sulphate,
• 4-amino-3-beta-(methanesulfonamido)ethyl-N,N-diethyl aniline hydrochloride and
• 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidene di-p-toluene sulfonic acid.

The concentration range of the hydroxylamine component is from 0.5 to 4 and especially from 0.5 to 2 g/l (as hydroxylamine sulphate).

The pH is preferably in the range 10.5 to 12 preferably 11 to 11.7.

The composition is preferably free of any compound that forms a dye on reaction with oxidised colour developer.

Conventional colour developer solutions for silver chloride colour papers do not contain hydroxylamine sulphate because it can act as a black and white developing agent and this severely inhibits dye yield. Instead, diethylhydroxylamine is used because it does not inhibit dye yield.

Conveniently the redox developer/amplifier solution used in the present invention comprises a colour developing agent, hydrogen peroxide or a compound which provides hydrogen peroxide and hydroxylamine or a salt thereof and wherein the concentration ranges are:

• hydrogen peroxide from 0.5 to 15 ml/l (as 30% w/w solution),
• hydroxylamine or a salt thereof from 0.25 to 8 g/l (as hydroxylamine sulphate),

For stable formulations the relative proportions of hydrogen peroxide (as ml/l of a 30% w/w solution) and hydroxylamine compound (as g/l hydroxylamine sulphate) may need to be balanced to give the required result. Because the process time is relatively short, this is optional for the redox developer/amplification solutions used in the present invention.

As previously stated the colour photographic material will contain more than 300mg/sq metre of silver, that is to say, they contain conventional amounts of silver rather than the low amounts of silver that are normally used in redox development.

A particular application of redox amplification is in the processing of silver chloride colour paper.

The material may comprise the emulsions, sensitisers, couplers, supports, layers, additives, etc. described in Research Disclosure, December 1978, Item 17643, published by Kenneth Mason Publications Ltd, Dudley Annex, 12a North Street, Emsworth, Hants P010 7DQ, U.K.

In a preferred embodiment the photographic material to be processed comprises a resin-coated paper support and the emulsion layers comprise more than 90% silver chloride and are more preferably composed of substantially pure silver chloride.

The photographic materials can be single colour materials or multicolour materials. Multicolour materials contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the materials, including the layers of the image-forming units, can be arranged in various orders as known in the art. A typical multicolour photographic material comprises a support bearing a yellow dye image-forming unit comprised of at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, and magenta and cyan dye image-forming units comprising at least one green- or red-sensitive silver halide emulsion layer having associated therewith at least one magenta or cyan dye-forming coupler respectively. The material can contain additional layers, such as filter layers.

As stated above, the process of the invention is particularly suitable for use in a tank of relatively small volume and in a preferred embodiment the ratio of the tank volume to maximum area of material accommodatable therein (i.e. maximum path length times width of material) is less than 11 dm³/m², preferably less than 3dm³/m².

The process may be carried out in what is known in the art as a minilab for example the tank volume may be below 5 litres and sometimes below 3.0 litres conveniently in the range 1.5 to 2.5 litres and may be about 1 litre.

The material to be processed is conveniently passed through the tank and preferably the developer solution is recirculated through the tank at a rate of 0.1 to 10 tank volumes per minute. The preferred recirculation rate is from 0.5 to 8 especially from 1 to 5 and particularly from 2 to 4 tank volumes per minute.

The recirculation with or without replenishment may be carried out continuously or intermittently. In one method of working both can be carried out continuously while processing is in progress but not at all or intermittently when the tank is idle.

Replenishment may be carried out by introducing the required amount of replenisher into the recirculation system either inside or outside the processing tank.

The shape and dimensions of the processing tank are preferably such that it holds the minimum amount of processing solution while still obtaining the required results. The tank is preferably one with fixed sides, the material being advanced therethrough by drive rollers. Preferably the photographic material passes through a thickness of solution of less then 11mm, preferably less than 5mm and especially about 2mm.

The shape of the tank-is not critical but it may conveniently be in the shape of a shallow tray or, preferably U shaped.

It is preferred that the dimensions of the tank be chosen so that the width of the tank is the same as or only just wider than the width of the material being processed.

The total volume of the processing solution within the processing channel and recirculation system is relatively smaller as compared with prior art processes. In particular the total amount of processing solution in the entire processing system for a particular module is such that the total volume in the processing channel is at least 40% of the total volume of the processing solution in the entire system. Preferably the volume of the processing channel is at least about 50% of the total volume of the processing solution in the system.

In order to provide efficient flow of the processing solution through the opening or nozzles into the processing channel, it is desirable that the nozzles/opening that deliver the processing solution to the processing channel have a configuration in accordance with the following relationship:$$\text{0.6 < F/A < 23}$$    where F is the flow rate of the solution through the nozzle in litres/minute and
   A is the cross sectional area of the nozzle provided in square centimetres.

Providing a nozzle in accordance with the foregoing relationship assures appropriate discharge of the processing solution against the photosensitive material.

Such low volume thin tank systems are described in more detail in the following patent specifications: US 5,294,956; 5,179,404; 5,270,762; EP559,025; 559,026; 559,027; WO92/10790; WO92/17819; WO93/04404; WO92/17370; WO91/19226; WO91/12567; WO9207302; WO93/00612 and WO92/07301.

The invention is illustrated by the following Examples.

All processing was carried out in the dark with 500ml measuring cylinders as tanks, placed in a tempered water bath. The exposed strips of paper were held in the appropriate tank by means of a clip for the required amount of time. Agitation of the strip was by manual lifting of the strip by 5cm and dropping again every 2 seconds turning the strip by 180° at the same time.

All the strips were exposed through 0.15 log exposure wedge for 1/10 of a second through a filter pack that has been determined to give neutral images with Kodak Ektacolor (Registered Trade Mark) Edge 2 paper processed through Kodak (Registered Trade Mark) Process RA-4.

For all experiments sensitometric parameters are given. These include Dmin (stain), D max, contrast and relative speed measured at 0.8 density units above Dmin for each colour layer.

A strip of exposed Kodak Ektacolor (Registered trade Mark) Edge 2 paper containing 600 to 700mg/m² of silver was processed in Kodak (Registered Trade Mark) Process RA-4 using chemicals made up to the tank concentrations as instructed.

The processing sequence was as follows: develop 45 seconds 35°C bleach-fix 45 seconds 35°C wash in running water 90 seconds 35°C

The resultant sensitometry is shown in Table 1. layer Dmin Dmax contrast relative speed red 0.094 2.59 3.72 129.1 green 0.103 2.62 3.42 124.2 blue 0.096 2.39 2.82 124.3

An experiment was carried out with the following developer and bleach-fix using the paper as in Example 1 Developer sequestrant 0.6g DTPA 0.81g K₂HPO₄.3H₂O 40.0g KBr 1.5mg KCl 0.45g Catechol disulfonate 0.3g Hydroxylamine sulfate 1.2g KOH (solid) 10.0g colour developer 5.5g Tween 80 (warmed) 0.3g dodecylamine (10% in glacial acetic acid) (dissolved in Tween) 1.0ml water to 1 litre pH adjusted to 11.5 with KOH solid Sequestrant used in all the examples was a 60% w/w aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid.

DTPA is diethylene triamine pentaacetic acid.

Colour developing agent used in all the Examples was N-(2-(4-amino-N-m-toluidino)ethyl)-methanesulfonamide sesquisulfate hydrate. bleach-fix NH₄FeEDTA (1.56 molar solution) 200ml ammonium thiosulfate 60g sodium metabisulfite 35g water to 1 litre pH adjusted to 5.5

EDTA is ethylene diamine tetraacetic acid.

The process cycle was as follows: develop 10 seconds 35°C bleach-fix 12 seconds 35°C wash in running water 12 seconds 35°C dry at room temperature

The experiment was also run with 0.8ml/l of hydrogen peroxide (30% w/w aqueous solution) added to the developer to demonstrate the ability of peroxide to accelerate the dye formation process and give adequate dye (matching the control) in a short time.

The results are shown in Table 2. process layer Dmin Dmax contrast relative speed no peroxide red 0.085 2.18 2.67 113.5 green 0.103 2.45 3.26 111.3 blue 0.099 1.78 2.14 100.0 with peroxide red 0.093 2.56 3.61 130.2 green 0.105 2.70 3.36 124.6 blue 0.100 2.42 2.92 120.3

The process without the peroxide was included for comparison.

The results show that the peroxide gives extra photographic speed, Dmax and contrast with only a slight stain penalty (as evidenced by the Dmin value) and allows a 10 second development step to match that of conventional paper with a 45 second development time (see Table 1 and Example 1). The whole wet part of the process can be achieved with agitation as described above in 34 seconds instead of 180 seconds (which is typical of the RA-4 process) and also avoid changes in sensitometry.

The paper was as in Example 1. The problem with an experiment to test this is that if silver halide is present in the paper, this will develop in the non-exposed areas and cause staining which will increase with the development time. It is necessary to separate out the staining in the bleach-fix which might be attributed to iron catalysed development in the presence of peroxide. In order to do this the silver was removed from the paper before processing by treating with a fixer of the following formula: ammonium thiosulfate 100g sodium sulfite 10g water to 1 litre

The paper was then washed to remove residual fixer.

The total process sequence was as follows: Fix 60 seconds 35°C Wash in running water 60 seconds 35°C Develop variable (see Table 3) 35°C Bleach-fix 12 seconds 35°C Wash in running water 12 seconds 35°C Dry at room temperature

The process was then carried out as before and the stains were recorded. The results are shown in Table 3. Development time (seconds) Red Dmin Green Dmin Blue Dmin 0 0.093 0.106 0.102 10 0.094 0.106 0.102 15 0.095 0.108 0.104 20 0.103 0.128 0.115 30 0.103 0.134 0.115 45 0.103 0.135 0.116 60 0.118 0.149 0.131

These results show that, under the conditions of this example, when a bleach fix step immediately follows a development/amplification step using peroxide, provided the time of the development/amplification step is 15 seconds or less, the stain as indicated by the Dmin value is kept to a low level.